1. Field of the Invention
The present invention relates to a printing apparatus which determines a video count value when a document image is combined with a copy-forgery-inhibited pattern image, a method of controlling the same, and a storage medium.
2. Description of the Related Art
In general, a developer density control device of an image forming apparatus adds up video count numbers of document image data to estimate the consumption of a developer for replenishment (for example, see Japanese Patent Application Laid-Open No. 04-221981). In order to generate image data that can produce effects similar to those of a forgery-inhibited sheet, there has recently been a technology of combining document image data with copy-forgery-inhibited pattern image data to generate print image data (for example, see Japanese Patent Application Laid-Open No. 2001-197297). In the case of combining document image data with copy-forgery-inhibited pattern image data, the developer consumption has conventionally been estimated for replenishment without adding up the combined video count numbers.
Copy-forgery-inhibited pattern image data includes regions to “remain” on a copy product and regions to “disappear” or become thinner than the regions to “remain”. The two types of regions have generally the same reflection densities on the original. This makes any embedded character string such as “COPY” less visible to the human eye. As employed herein, to “remain” means that an image on an original is reproduced on a copy product. To “disappear” means that an image on an original is thinly reproduced, or not reproduced, on a copy product.
Hereinafter, regions to “remain” on a copy product will be referred to as “latent image portions.” Regions to “disappear” or become thinner than regions to “remain” will be referred to as “background portions.”
FIG. 7 is a diagram illustrating a state of dots in copy-forgery-inhibited pattern image data. The region where dots are concentrated is a latent image portion. The region where dots are dispersed is a background portion. In the two regions, dots are generated by respective different types of halftone dot processing and/or different types of dither processing. For example, the dots in the latent image portion are generated by halftone dot processing with a low screen ruling. The dots in the background portion are generated by halftone dot processing with a high screen ruling. Alternatively, the dots in the latent image portion may be generated by using a dot-concentrated-type dither matrix. The dots in the background portion may be generated by using a dot-dispersed-type dither matrix.
A copying machine's reproduction capability depends on the input resolution and output resolution of the copying machine. There is, therefore, a limit to the copying machine's reproduction capability. Suppose that dots in a latent image portion of copy-forgery-inhibited pattern image data are formed to be larger than reproducible dots of a copying machine, and dots in a background portion are formed to be smaller than the reproducible dots. In such a case, the dots in the latent image portion are typically reproduced while those in the background portion are less likely to be. As a result, the latent image portion is reproduced thicker than the background portion on a copy product. Hereinafter, the phenomenon that latent image portions are reproduced thicker than background portions on a copy product so that an embedded character string or the like appears to be visible will be referred to as visualization.
FIGS. 8A and 8B are diagrams illustrating the visualization. The diagrams conceptually illustrate that concentrated dots (large dots) are reproduced on a copy product while dispersed dots (small dots) are not accurately reproduced on the copy product.
Copy-forgery-inhibited pattern image data is not limited to the foregoing configuration. Copy-forgery-inhibited pattern image data may have any configuration as long as a character string such as “COPY” or a symbol or pattern appears (is visualized) on a copy product so as to be recognizable to humans. A character string like “COPY” may be shown in outline on a copy product, and such copy-forgery-inhibited pattern image data is also applicable. In such a case, the regions of “COPY” will be referred to as background portions.
A copy-forgery-inhibited pattern is composed of background portions and latent image portions. It is important that the two types of regions be rendered in generally the same reflection densities on an original.
According to the conventional technology, outputting image data in which document image data and copy-forgery-inhibited pattern image data are combined inevitably causes small errors between the developer's consumption system and replenishment system. Such small errors can be accumulated to gradually change the mixing ratio of a developer, i.e., toner and a carrier. This makes image output with an optimum density impossible.